Electronic amplifiers are often based on a class-A or class-AB principle in which an analog signal is amplified continuously in the single-phase or push-pull action by means of amplification elements, such as transistors. Today, however, electronic amplifiers that operate according to the class-D principle are increasingly being used. Such amplifiers could also be called switching amplifiers. In such amplifiers, an analog signal is converted, for example, by comparison with a triangular oscillation into a pulse-width-modulated, PWM signal. By means of the pulse-width-modulated signal, an active element is driven that couples supply connections to an output. Through the switching action, the efficiency of such an amplifier is improved relative to continuously amplifying amplifiers.
The signal processing within the switching amplifier here, however, depends on an available supply voltage. For example, the signal from which the pulse-width-modulated signal is derived can assume a level in which a constant signal that leads to distortion on the amplifier output is produced on the output of a PWM modulator used for this purpose. In addition, a loudspeaker that is connected, for example, to the amplifier output, could be damaged or destroyed by this constant signal. Furthermore, this could result in an unfavorable total harmonic distortion, THD, of the amplifier.
As a countermeasure, for example, additional pulses could be inserted into the PWM signal, wherein, however, the actual signal to be amplified is distorted. Alternatively, an input level of the PWM modulator could also be limited as a function of a minimum available supply voltage. However, through this measure, the input signal to be amplified is also reduced, which leads to a lower output power across the entire supply-voltage range.